Electrical switch



June 2, 1936. s. RUTTENBERG ELECTRICAL SWITCH Filed May 12, 1933 I INVENTOR 2 ATTORNEY Patented June 2, 1936 UNITED STATES PATENT OFFICE 3 Claims.

. This invention relates to a protected indicating circuit. Specifically it relates to the combination of a thermostatic protective device and a sensitive electrical measuring instrument.

An object 01 the invention is to provide in combination with an electrical meter, a thermostatically operated protective relay to protect the meter from the effects of excessive currents.

Further objects will be apparent from the dis closure and from the drawing which illustrates a thermal relay in series with a voltmeter and a source of potential.

Generally it may be stated that the invention comprehends the use of a vacuum type relay in series with a sensitive electrical measuring instrument, the relay utilizing the expansion of a small diameter resistance wire to move a contact which opens the circuit.

Electrical measuring instruments generally use a fine copper wire magnetic coil and if the device should be subjected to a relatively high voltage or current, the overheating of the coil results in injury to the meter. Fusing of the meter is impracticable with very sensitive instruments, due to the fact that excess currents of the degree encountered, are insufficient to actuate the fuse.

In the device of my invention, the current which flows through the coil must pass through a short length of resistance wire, preferably of the nickel-chromium type. If an excess current is applied to the meter, which under ordinary circumstances would cause the meter to blow, the temperature rise, caused by this excess current, eiiects a thermal expansion of the resistance wire which pushes a movable contact away from the stationary contact.

I prefer to operate the contact device or relay in a vacuum or in other inert and non-oxidizing atmospheres. This insures freedom from oxidation, reduction of heating current, increased sensitivity and elimination of arcing.

In order to describe a form of the invention in a detailed manner, reference is made to the accompanying drawing in which the evacuated tube ('1') houses a nickel support (I) on which is welded fiat spring (2) which serves as the movable contact and on which is a supporting element (3) for the nickel-chromium expansion wire (4). Stationary contact (5) is mounted on one terminal (6) which extends through the tube. The nickel chromium wire (4) l is supported by the terminal (1) which also projects through the tube T. At (8) is the press for supporting the extended terminals (6) and (1). In the circuit,

the coil of the voltmeter V is in series with the relay and the source of potential E.

When the unit is assembled, the wire (4) is pulled downward until it moves the flat spring (2) which causes its lower end to contact with contact (5). The lower end of the wire (4) is then welded to support (1).

The resistance value of the wire (4) is so fixed that if an excess current is discharged through it, the heat causes an expansion which releases the tension of upper support end (3) of flat spring (2) and the contact opens. This action occurs intermittently as long as the excess current value is had. This value is determined by the mass of the wire, its length, resistance and spring tension. A suitable Wire element is one composed of a nickel chromium alloy, approximately long, approximately .002 in diameter and having a resistance under 20 ohms, preferably about 12 ohms.

I claim:-

1. A switch comprising a sealed envelope having therewithin a support element, a spring attached to said support constituting part of a movable contact element, a normally tensioned thermo expansible wire attached to said spring and constituting a current carrying member and a stationary contact adapted to cooperate with the movable contact element to maintain a closed circuit within the envelope, said thermo-expansibie wire under normal current carrying conditions serving to keep said circuit closed but under excessive current conditions adapted to become untensioned so as to allow a movement of the movable contact and the opening of said circuit.

2. A switch comprising an evacuated sealed envelope having therewithin a support element, a fiat spring afiixed thereto, constituting part of a movable contact element, a fine dimension normally tensioned thermo-expansible nickel chromium Wire and constituting a current carrying member, a supporting member connecting said wire to said flat spring, an additional supporting member for said wire adapted to conduct electrical current thereto, a stationary contact element adapted to cooperate with the movable contact element to maintain a closed circuit within the envelope and an electrical conductor element to lead current to said stationary contact, said thermo-expansible wire under normal current carrying conditions serving to keep said circuit closed but under excessive current conditions adapted to become untensioned so as to allow a movement of. the movable contact and the opening of said circuit.

.a. current carrying 3. A switch comprising an evacuated sealed envelope having therewithin a. nickel support element sealed into the stem of said envelope, :1 flat spring aflixed thereto constituting a movable contact element, a, normally tensioned thermo-' expansible resistance wire not substantially greater than .002" in diameter and constituting member, a supporting member connecting said wire to said flat spring, an additional support member for said wire for conducting electrical current thereto, a stationary circuit.

SAMUEL R. 

